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Cell Growth & Division

Here we see the life cycle of a somatic cell, otherwise known as the cell cycle. It is comprised of two phases - interphase and the mitotic phase. Interphase is divided into three periods: G1, S, and G2.

G1 is referred to as the pre-DNA synthesis period. Intense growth and metabolic activity take place during this phase. At the end of G1, the cell must go through a "checkpoint". This G1/S checkpoint verifies either that sufficient time has elapsed since the preceding mitosis or that the cell has attained an appropriate size for DNA replication to be initiated.

The cell next proceeds to the S phase, in which DNA replication and protein synthesis take place. During this phase, an exact copy of each chromosome is made. These copies are referred to as sister chromatids.

Finally, the cell reaches G2, the third period in interphase. In this, the shortest of the three periods, the synthesis of organelles and materials required for cell division takes place. Basically, this period gets the cell prepped for Mitosis.

Before mitosis can begin, a second checkpoint must be passed. This is the G2/M checkpoint. It requires that DNA replication be complete and that any DNA damage be repaired before the cell can move on to mitosis.

Last of all is the M phase, in which mitosis, the process by which the cell's nucleus divides into two nuclei, takes place. After mitosis, cytokinesis produces two daughter cells, each of which have the same number and kinds of chromosomes as the parent cell.